Antinuclear antibodies are a hallmark of autoimmune disease. This research is directed toward the characterization of the nuclear proteins that serve as indicators of various rheumatic diseases, including systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD). Two such antigens have been designated Sm and RNP. Together these antigens are represented by at least 10 polypeptides, all of which are part of larger particles called the snRNP (small nuclear ribonucleoprotein). Characterization of these antigens will cover the spectrum from immunoreactive polypeptide to constituent snRNP complexes. Emphasis is being placed on individual polypeptides to use them as the basis for the development of specific and quantitative diagnostic/prognostic assays for the Sm and RNP antibodies. To that end a major continuing emphasis in this laboratory is the use of recombinant DNA technology for the cDNA cloning and expression of the relevant antigens. The availability of cDNA clones and recombinant polypeptides will also allow for a critical assessment of multiple Sm and RNP polypeptides at various levels to aid in the delineation of both antigen and snRNP structure. These studies will include at the genomic level: discrimination of closely related polypeptides; Northern blot analyses to characterize specific mRNA species; sequencing of the intact gene. Detailed antigen analysis will be facilitated by: epitope mapping; interspecies comparisons at both the peptide and genomic (Southern blot analysis) levels; exploration of possible relationships between these antigens and infectious agents. Studies will continue on the snRNP complexes associated with these antigens, with particular emphasis on the isolation of individual snRNP particles, as well as studies of protein-protein and protein-RNA interactions; all of which will provide information as to the assembly of the functional particle. A corollary to these studies is the continued production of monoclonal and polyclonal antibodies with utility as molecular probes. Lastly these studies will be expanded to include other nuclear proteins synonymous with autoimmune antigens, in particular hnRNP and nuclear matrix proteins. Overall these studies are asking what features make antigens such as Sm and RNP targets in the autoimmune sequence of events, while relating these same polypeptides to the native cellular environment in which they function.